1. Field of the Invention
This invention concerns antioxidant compositions, especially antioxidant compositions for gasoline. The compositions comprise primarily hindered phenols in combination with a small amount of an amine. The compositions are characterized by reduced crystallization temperature, lighter color, and enhanced antioxidant efficiency, over compositions that are similar except that they do not have the amine present.
2. Description of the Prior Art
Phenolic antioxidants are preferred for modern gasolines which have relatively low olefin content, because of their low cost and increasing relative antioxidant efficiency with decreasing olefin content of the gasoline. Principal commercially employed antioxidants are the alkylated phenols, N,N'-dialkylated para-phenylenediamines and N-alkylated para-aminophenols.
Alkylated phenol antioxidants usually contain a tertiary alkyl group ortho to the hydroxyl group. Included are 2,6-ditert.-butyl-4-methylphenol, 2,4-dimethyl-6-tert.-butylphenol, 2,4-ditert.-butylphenol, 2,6-ditert.-butylphenol, 2-tert.-butylphenol, 4,4'-methylene-bis(2,6-ditert.-butylphenol), 4,4'-thiobis(2,6-ditert.-butylphenol) and the like. Such phenols containing the bulky tertiary alkyl group at one or both ortho positions are often referred to as hindered phenols.
Most hindered phenols are solids at ambient temperatures or they are liquids which crystallize when exposed to low temperatures such as are encountered during the winter months in colder climates. It is generally preferred that a gasoline additive be liquid for ease of addition and lower costs. Using solvents to provide hindered phenol as concentrated solutions is not completely satisfactory since the phenols are still subject to crystallization from solution at low temperatures. Further, the increased cost of preparing, handling and shipping solutions makes this unattractive. There is, therefore, a need for a practical liquid hindered phenol antioxidant composition which is resistant to solidification (crystallization) at relatively low temperatures. Also desirable would be for such composition to have good light color and good efficiency.